Imaging geometry for image-guided radiosurgery

ABSTRACT

A system and method for stereoscopically imaging a patient at multiple locations in a radiation treatment system with variable imaging geometry to enable the delivery of radiation treatments from multiple ranges of treatment angles without obstructing the imaging system or the radiation treatment.

This application is a continuation application of U.S. patentapplication Ser. No. 11/170,832, filed Jun. 29, 2005, now U.S. Pat. No.7,302,033 which is herein incorporated by reference.

TECHNICAL FIELD

The present invention relates generally to image-guided radiationtreatment systems and, in particular, to the geometry of imaging systemsfor guiding radiation treatment.

BACKGROUND

Radiosurgery and radiotherapy are radiation treatment systems that useexternal radiation beams to treat pathological anatomies (e.g., tumors,lesions, vascular malformations, nerve disorders, etc.) by delivering aprescribed dose of radiation (e.g., X-rays or gamma rays) to thepathological anatomy while minimizing radiation exposure to surroundingtissue and critical anatomical structures (e.g., the spinal chord). Bothradiosurgery and radiotherapy are designed to necrotize pathologicalanatomy while sparing healthy tissue and the critical structures.Radiotherapy is characterized by a low radiation dose per treatment andmany treatments (e.g., 30 to 45 days of treatment). Radiosurgery ischaracterized by a relatively high radiation dose in one, or at most afew, treatments. In both radiotherapy and radiosurgery, the radiationdose is delivered to the site of the pathological anatomy from multipleangles. As the angle of each radiation beam is different, each beamintersects a target region occupied by the pathological anatomy, butpasses through different areas of healthy tissue on its way to and fromthe target region. As a result, the cumulative radiation dose in thetarget region is high and the average radiation dose to healthy tissueand critical structures is low.

Frame-based radiotherapy and radiosurgery treatment systems employ arigid, invasive stereotactic frame to immobilize a patient duringpretreatment imaging for diagnosis and treatment-planning (e.g., using aCT scan or other 3-D imaging modality, such as MRI or PET), and alsoduring subsequent radiation treatments. These systems are limited tointracranial treatments because the rigid frame must be attached to bonystructures that have a fixed spatial relationship with target region,and the skull and brain are the only anatomical features that satisfythat criterion.

In one type of frame-based radiosurgery system, a distributed radiationsource (e.g., a cobalt 60 gamma ray source) is used to produce anapproximately hemispherical distribution of simultaneous radiation beamsthough holes in a beam-forming assembly. The axes of the radiation beamsare angled to intersect at a single point (treatment isocenter) and thebeams together form an approximately spherical locus of high intensityradiation. The distributed radiation source requires heavy shielding,and as a result the equipment is heavy and immobile. Therefore, thesystem is limited to a single treatment isocenter.

In another type of frame-based radiotherapy system, known as intensitymodulated radiation therapy (IMRT), the radiation treatment source is anx-ray beam device (e.g., a linear accelerator) mounted in a gantrystructure that rotates around the patient in a fixed plane of rotation.IMRT refers to the ability to shape the cross-sectional intensity of theradiation beam as it is moved around the patient, using multi-leafcollimators (to block portions of the beam) or compensator blocks (toattenuate portions of the beam). The axis of each beam intersects thecenter of rotation (the treatment isocenter) to deliver a dosedistribution to the target region. Because the center of rotation of thegantry does not move, this type of system is also limited to a singletreatment isocenter.

Image-guided radiotherapy and radiosurgery systems (together,image-guided radiation treatment (IGRT) systems) eliminate the need forinvasive frame fixation by tracking changes in patient position betweenthe pre-treatment imaging phase and the treatment delivery phase(in-treatment phase). This correction is accomplished by acquiringreal-time stereoscopic X-ray images during the treatment delivery phaseand registering them with reference images, known as digitallyreconstructed radiograms (DRRs), rendered from a pre-treatment CAT scan.A DRR is a synthetic X-ray produced by combining data from CAT scanslices and computing a two-dimensional (2-D) projection through theslices that approximates the geometry of the real-time imaging system.

Gantry-based IGRT systems add an imaging x-ray source and a detector tothe treatment system, located in the rotational plane of the LINAC(offset from the LINAC, e.g., by 90 degrees), and which rotate with theLINAC. The imaging x-ray beam passes through the same isocenter as thetreatment beam, so the imaging isocenter coincides with the treatmentisocenter, and both isocenters are fixed in space.

FIG. 1 illustrates the configuration of an image-guided, robotic-basedradiation treatment system 100, such as the CYBERKNIFE® RadiosurgerySystem manufactured by Accuray, Inc. of California. In this system, thetrajectories of the treatment x-ray beams are independent of thelocation of the imaging x-ray beams. In FIG. 1, the radiation treatmentsource is a LINAC 101 mounted on the end of a robotic arm 102 havingmultiple (e.g., 5 or more) degrees of freedom in order to position theLINAC 101 to irradiate a pathological anatomy (target region or volume)with beams delivered from many angles, in many planes, in an operatingvolume around the patient. Treatment may involve beam paths with asingle isocenter, multiple isocenters, or with a non-isocentric approach(i.e., the beams need only intersect with the pathological target volumeand do not necessarily converge on a single point, or isocenter, withinthe target).

In FIG. 1, the imaging system includes X-ray sources 103A and 103B andX-ray detectors (imagers) 104A and 104B. Typically, the two x-raysources 103A and 103B are mounted in fixed positions on the ceiling ofan operating room and are aligned to project imaging x-ray beams fromtwo different angular positions (e.g., separated by 90 degrees) tointersect at a machine isocenter 105 (where the patient will be locatedduring treatment on a treatment couch 106) and to illuminate imagingsurfaces (e.g., amorphous silicon detectors) of respective detectors104A and 104B after passing through the patient. FIG. 2 illustrates thegeometry of radiation treatment system 100. Typically, the x-raydetectors 104A and 104B are mounted on the floor 109 of the operatingroom at ninety degrees relative to each other and perpendicular to theaxes 107A and 107B of their respective imaging x-ray beams. Thisorthogonal, stereoscopic imaging geometry is capable of great precision,reducing registration errors to sub-millimeter levels. However, thereare some inherent limitations associated with this imaging geometry wheninstalled in a typical operating room, which may have a ceiling no morethan nine or ten feet high.

As illustrated in FIG. 2, the LINAC 101 is highly maneuverable andrelatively compact, but it still requires a minimum amount of separationbetween the patient 108 and the ceiling 110 of the operating room todeliver treatments from above the patient. There are also certainpositions that the LINAC may be unable to occupy, either because theLINAC may block one of the imaging x-ray beams or because one of thex-ray detectors may block the radiation treatment beam. Furthermore,because the patient must be located at least some minimum distance fromthe ceiling to enable access from above, there may be insufficient roombelow the patient to deliver treatment from below, even if treatmentfrom under the patient would be more beneficial (e.g., treating thespinal area while the patient is laying face up). Therefore, thelocation of the imaging center of the imaging system may need to bechosen as a compromise between treatment access and imaging access.

BRIEF DESCRIPTION OF THE FIGURES

The present invention is illustrated by way of example, and not bylimitation, in the figures of the accompanying drawings in which:

FIG. 1 illustrates a conventional image-guided radiation treatmentsystem;

FIG. 2 illustrates the geometry of a conventional image-guided radiationtreatment system;

FIG. 3A illustrates an imaging system in one embodiment of imaginggeometry;

FIG. 3B illustrates one application of the embodiment of FIG. 3A;

FIG. 3C illustrates another application of the embodiment of FIG. 3A;

FIGS. 4A and 4B illustrate an imaging system in a second embodiment ofimaging geometry;

FIG. 5 illustrates an imaging system in a third embodiment of imaginggeometry;

FIG. 6 illustrates an imaging system in a fourth embodiment of imaginggeometry;

FIG. 7 illustrates an imaging system in a fifth embodiment of imaginggeometry;

FIG. 8A illustrates an imaging system in a sixth embodiment of imaginggeometry;

FIGS. 8B and 8C illustrate a treatment delivery system incorporating theembodiment of FIG. 8A.

FIGS. 9A and 9B illustrate an imaging system in a seventh embodiment ofimaging geometry;

FIG. 10 is a flowchart illustrating a method in one embodiment ofimaging geometry;

FIG. 11 illustrates a system in which embodiments of imaging geometrymay be practiced; and

FIG. 12 is a flowchart illustrating a method in one embodiment ofimaging geometry.

DETAILED DESCRIPTION

Apparatus and methods for imaging geometry in radiation treatmentsystems are described. In the following description, numerous specificdetails are set forth such as examples of specific components, devices,methods, etc., in order to provide a thorough understanding ofembodiments of the present invention. It will be apparent, however, toone skilled in the art that these specific details need not be employedto practice embodiments of the present invention. In other instances,well-known materials or methods have not been described in detail inorder to avoid unnecessarily obscuring embodiments of the presentinvention. The term “coupled” as used herein, may mean directly coupledor indirectly coupled through one or more intervening components orsystems. The term “X-Ray image” as used herein may mean a visible X-rayimage (e.g., displayed on a video screen) or a digital representation ofan X-ray image (e.g., a file corresponding to the pixel output of anX-ray detector). The terms “in-treatment image” or “real-time image” asused herein may refer to images captured at any point in time during atreatment delivery phase of a radiosurgery or radiotherapy procedure,which may include times when the radiation source is either on or off.The term IGR as used herein may refer to image-guided radiation therapy,image-guided radiosurgery, or both.

FIG. 3A illustrates an imaging system 300 in one embodiment of animaging geometry associated with a robotic-based IGRT system such as theCYBERKNIFE® Radiosurgery System, manufactured by Accuray, Inc. ofCalifornia. Imaging system 300 includes a first pair of x-ray sources301A and 301B to generate a first x-ray beam 302A and a second x-raybeam 302B, where the axis 303A of the first x-ray beam and the axis 303Bof the second x-ray beam define a first imaging plane. Imaging system300 may also include a second pair of x-ray sources 301C and 301D togenerate a third x-ray beam 302C and a fourth x-ray beam 302D, where theaxis 303C of the third x-ray beam and the axis 303D of the fourth x-raybeam define a second imaging plane. The first x-ray beam 302A and thesecond x-ray beam 302B may be disposed to intersect at a first angle β₁at a first imaging center 304. The third x-ray beam 302C and the fourthx-ray beam 302D may be disposed to intersect at a second angle β₂ at asecond imaging center 305. Imaging system 300 may also include a firstpair of x-ray detectors 306A and 306B in the first imaging plane todetect the first x-ray beam 302A and the second x-ray beam 302B, and asecond pair of x-ray detectors 306C and 306D in the second imaging planeto detect the third x-ray beam 302C and the fourth x-ray beam 302D.

Thus, as illustrated in FIG. 3A, the imaging geometry of imaging system300 may provide two imaging centers 304 and 305 located at differentelevations. X-ray sources 301A and 301B may be located above the imagingcenters and x-ray sources 301C and 301D may be located below the imagingcenters. Angles β₁ and β₂ may be selected (e.g., by changing theseparation between the x-ray sources and/or the x-ray detectors) todetermine the location of the imaging centers with respect to oneanother and with respect to the x-ray sources and x-ray detectors. Inparticular, angles β₁ and β₂ may be selected to be equal angles (e.g.,90 degrees) such that the intersection of x-ray beam 302A and x-ray beam302B is symmetrical with the intersection of x-ray beams 302C and 302D.

Two imaging centers, such as imaging centers 304 and 305, may establishmultiple treatment frames of reference and enable image-guided radiationtreatment from above a patient and from below a patient. For example, asillustrated in FIG. 3B, x-ray sources 301A and 301B, and x-ray detectors306C and 306D may be mounted on the ceiling 307 of an operating room.X-ray sources 301C and 301D, and x-ray detectors 306A and 306B may bemounted on the floor 308 of the operating room. If a patient 309 ispositioned (e.g., by moving the patient on a robotic couch, such astreatment couch 310) near the first machine center 304, the patient maybe imaged while a robotically controlled LINAC 311 administers radiationtreatment from a region 312 above the patient. Region 312 may include apredefined set of treatment nodes or locations where LINAC 311 may bepositioned to deliver radiation treatment from one or more angles. Forexample, region 312 may include 100 nodes and LINAC 311 may bepositioned at 12 different angles at each node to deliver a total of1200 individual treatment beams. In one embodiment, in the case ofintracranial radiation treatment, for example, region 312 may be anapproximately hemispherical region centered on the head of patient 309with a radius from approximately 650 millimeters to approximately 800millimeters. In an alternative embodiment, in the case of radiationtreatment to the body of patient 309, region 312 may be an approximatelycylindrical with a radius from approximately 900 mm to 1000 mm.Conversely, as illustrated in FIG. 3C, if the patient 309 is positionednear the second machine center 305, the patient may be imaged while therobotically controlled LINAC 311 administers radiation treatment from aregion 313 below the patient which may mirror the same generaldimensions as region 312.

FIG. 3A illustrates an imaging system 300 where the first imaging planeand the second imaging plane are coplanar planes. Other configurationsof the first imaging plane and the second imaging plane may beadvantageous (e.g., to best utilize limited floor space in an operatingroom or to reduce the number of blocked treatment nodes). FIG. 4Aillustrates an alternative embodiment of a system 400 where the firstimaging plane 314 is rotated at an angle γ with respect to the secondimaging plane 315. In one embodiment, as illustrated in FIG. 4B as a topdown view of system 400, γ may be a ninety degree angle. FIG. 4Billustrates how treatment couch 310 may be positioned at multiple angleswith respect to LINAC 311 on robotic arm 318, with respect to imageplanes 314 and 315, and also with respect to machine centers 304 and305. It will be appreciated that the positioning flexibility provided bythe configuration of system 400 may eliminate the problem of blockedtreatment nodes described above.

Returning now to FIG. 3A, it will be observed that x-ray detector 306Amay be disposed at an imaging angle θ₁ with respect to the axis 303A ofx-ray beam 302A. Likewise, x-ray detectors 306B, 306C and 306D may bedisposed at imaging angles θ₂, θ₃ and θ_(4 with) respect to the axes303B, 303C and 303D of x-ray beams 302B, 302C and 302D. In oneembodiment, imaging angles θ₁ through θ₄ may be ninety degree angles,such that the imaging surfaces of x-ray detectors 306A through 306D areall perpendicular to the axes of their respective x-ray beams. Inanother embodiment, imaging angles θ₁ through θ₄ may be acute anglesselected to dispose x-ray detectors 306A and 306B along a baseline 316in the first imaging plane 314, and to dispose x-ray detectors 306C and306D along a topline 317 in the second imaging plane 315. In oneembodiment, baseline 316 and topline 317 may correspond to the ceiling307 and the floor 308 of FIGS. 3B and 3C.

In one embodiment of imaging geometry, as illustrated in FIG. 5, animaging system 500 may include three x-ray sources and three x-raydetectors. In FIG. 5, a first x-ray source 501A may project an x-raybeam 502A, having an axis 503A, onto an imaging surface 508A of a firstx-ray detector 506A. A second x-ray source 501B may project an x-raybeam 502B, having an axis 503B, onto an imaging surface 508B of a secondx-ray detector 506B. X-ray beam 502B may be disposed to intersect x-raybeam 502A such that axis 503B intersects axis 503A at a first imagingcenter 504 at an angle α₁. A third x-ray source 501C may project a thirdx-ray beam, having an axis 503C, onto an imaging surface 508C of a thirdx-ray detector 506C. X-ray beam 502C may be disposed to intersect x-raybeam 502A such that axis 503C intersects axis 503A at a second imagingcenter 505 at a second angle α₂. X-ray beam 502C may also be disposed tointersect x-ray beam 502B such that axis 503C intersects axis 503B at athird imaging center 507 at an angle α₃.

In one embodiment, imaging surface 508A may be disposed at an imagingangle φ₁ with respect to axis 503A, imaging surface 508B may be disposedat an imaging angle φ₂ with respect to axis 503B, and imaging surface508C may be disposed at an imaging angle φ₃ with respect to axis 503C.In one embodiment, angles φ₁, φ₂ and φ₃ may be right angles. In otherembodiments, one or more of angles φ₁, φ₂, and φ₃ may be selected suchthat imaging surfaces 508A, 508B and 508C are parallel to a baseline509.

In one embodiment, x-ray source 501A and x-ray detector 506A may each beconfigured to move horizontally, together or independently, in order toadjust the points of intersection of the first x-ray beam 502A with thesecond x-ray beam 502B and the third x-ray beam 502C, in order to adjustthe locations of the first imaging center 504 and the second imagingcenter 505, and/or the separation A between the first imaging center 504and the second imaging center 505.

FIG. 6 illustrates an imaging system 600 in yet another embodiment ofimaging geometry. Imaging system 600 includes a first pair of x-raysources 601A and 601B at a separation δ₁ to project a first x-ray beam602A and a second x-ray beam 602B to intersect at an angle ρ₁ at a firstimaging center 604, located at a height h₁ above the x-ray sources.Imaging system 600 may also include a second pair of x-ray sources 601Cand 601D at a separation δ₂ to project a third x-ray beam 602C and afourth x-ray beam 602D to intersect at an angle ρ₂ at a second imagingcenter 605, located at a height h₂ above the x-ray sources. Separationsδ_(1,) δ₂ and δ₃ may be selected to adjust the angles ρ₁ and ρ_(2,) andthe locations of imaging centers 604 and 605. As illustrated in FIG. 6,imaging center 604 is enclosed by an imaging volume V₁, subtended byx-ray beams 602A and 602B. Imaging center 605 is enclosed by an imagingvolume V₂, subtended by x-ray beams 602C and 602D. Volumes V1 and V2 mayalso be adjusted by selecting separations δ_(1,) δ_(2,) and δ₃. Althoughnot illustrated, it will be appreciated that the geometry of FIG. 6 maybe inverted. That is, the locations of the x-ray sources and x-raydetectors may be reversed.

FIG. 7 illustrates a system 700 in another embodiment of imaginggeometry. System 700 includes a single pair of movable x-ray sourceswhich may be configured to maintain alignment with x-ray detectors 606Aand 606B when x-ray sources 701A and 701B are at either separation δ₁ orδ₂. Methods for maintaining angular alignments through lineardisplacements are known in the art and will not be described, herein.Thus, it will be appreciated that imaging system 700 may provide thesame functionality as imaging system 600 with only two x-ray sources.

FIG. 8A illustrates an imaging system 800 in another embodiment ofimaging geometry. Imaging system 800 includes two pairs of x-ray sources801A and 801B, and 801C and 801D mounted below a floorline 808 andcovered by an x-ray transparent material 809. It will be appreciatedthat mounting the x-ray sources below the floorline may maximize thespace available within an operating theater to position a LINAC, such asLINAC 311 for treatment. X-ray sources 801A and 801B may project x-raybeams 802A and 802B that intersect at imaging center 804 and illuminatex-ray detectors 806A and 806B, respectively. X-ray sources 801C and 801Dmay project x-ray beams 802C and 802D that intersect at imaging center805 and illuminate x-ray detectors 806A and 806B, respectively.

FIGS. 8B and 8C illustrate an example of a radiation treatment deliverysystem 825 incorporating the imaging system of FIG. 8A. Radiationtreatment delivery system 825 includes a LINAC 311 mounted on a roboticarm 810. The system also includes a robotic arm assembly 811, withmultiple degrees of freedom of motion (e.g., five or more) to positiontreatment couch 310 at multiple positions relative to imaging centers804 and 805. FIG. 8B illustrates treatment couch 310 positioned inproximity to imaging center 804, and FIG. 8C illustrates treatment couch310 positioned in proximity to imaging center 805.

FIGS. 9A and 9B illustrate an imaging system 900 in a further embodimentof imaging geometry. Imaging system 900 includes a pair of movable x-raysources 901A and 901B which may be linearly translated to change theseparation between the x-ray sources from σ₁ to σ₁′. Imaging system 900may also include a pair of movable x-ray detectors 906A and 906B whichmay be linearly translated to change the separation between the x-raydetectors from σ₂ to σ₂′. In FIG. 9A, x-ray beams 902A and 902Bintersect at image center 904. At the position of the x-ray sources andx-ray detectors illustrated in FIG. 9 a, it can be seen that treatmentcannot be provided by LINAC 911 (shown in dotted line) becausepositioning the LINAC as shown will block x-ray beam 902B and preventimaging system 900 from obtaining a stereoscopic image. FIG. 9Billustrates imaging system 900 with x-ray sources 901A and 901B, andx-ray detectors 906A and 906B, repositioned to generate x-ray beams thatintersect at imaging center 904 without being blocked by LINAC 911.

FIG. 10 is a flowchart illustrating a method 925 in one embodiment of animaging geometry. With reference to FIGS. 3A-3C and 4A, the methodincludes establishing a first imaging center 304 at a first location h1to enable radiation treatment of a target anatomy 309 from a firstregion 312 in a treatment frame of reference (step 1001). The methodalso includes establishing a second imaging center 305 at a secondlocation h2 to enable radiation treatment of the target anatomy 309 froma second region 313 in the treatment frame of reference (step 1002).

In one embodiment, establishing the first imaging center (step 1001) mayinclude generating a first imaging beam 302A having a first axis 303A,and a second imaging beam 302B having a second axis 303B, the first axisand the second axis defining a first image plane 314, the second imagingbeam disposed at a first angle β₁ with respect to the first imaging beamto intersect the first imaging beam at the first location. In oneembodiment, establishing the second imaging center (step 1002) mayinclude generating a third imaging beam 302C having a third axis 303C,and a fourth imaging beam 302D having a fourth axis 303D, the third axisand the fourth axis defining a second image plane 315, the fourthimaging beam disposed at a second angle β₂ with respect to the thirdimaging beam to intersect the third imaging beam at the first location.

FIG. 11 illustrates one embodiment of systems that may be used inperforming radiation treatment in which features of the presentinvention may be implemented. As described below and illustrated in FIG.10, system 4000 may include a diagnostic imaging system 1000, atreatment planning system 2000 and a treatment delivery system 3000.

Diagnostic imaging system 1000 may be any system capable of producingmedical diagnostic images of a volume of interest (VOI) in a patientthat may be used for subsequent medical diagnosis, treatment planningand/or treatment delivery. For example, diagnostic imaging system 1000may be a computed tomography (CT) system, a magnetic resonance imaging(MRI) system, a positron emission tomography (PET) system, a singlephoton emission CT (SPECT), an ultrasound system or the like. For easeof discussion, diagnostic imaging system 1000 may be discussed below attimes in relation to a CT x-ray imaging modality. However, other imagingmodalities such as those above may also be used.

Diagnostic imaging system 1000 includes an imaging source 1010 togenerate an imaging beam (e.g., x-rays, ultrasonic waves, radiofrequency waves, etc.) and an imaging detector 1020 to detect andreceive the beam generated by imaging source 1010, or a secondary beamor emission stimulated by the beam from the imaging source (e.g., in anMRI or PET scan). In one embodiment, diagnostic imaging system 1000 mayinclude two or more diagnostic X-ray sources and two or morecorresponding imaging detectors. For example, two x-ray sources may bedisposed around a patient to be imaged, fixed at an angular separationfrom each other (e.g., 90 degrees, 45 degrees, etc.) and aimed throughthe patient toward (an) imaging detector(s) which may be diametricallyopposed to the x-ray sources. A single large imaging detector, ormultiple imaging detectors, can also be used that would be illuminatedby each x-ray imaging source. Alternatively, other numbers andconfigurations of imaging sources and imaging detectors may be used.

The imaging source 1010 and the imaging detector 1020 are coupled to adigital processing system 1030 to control the imaging operation andprocess image data. Diagnostic imaging system 1000 includes a bus orother means 1035 for transferring data and commands among digitalprocessing system 1030, imaging source 1010 and imaging detector 1020.Digital processing system 1030 may include one or more general-purposeprocessors (e.g., a microprocessor), special purpose processor such as adigital signal processor (DSP) or other type of device such as acontroller or field programmable gate array (FPGA). Digital processingsystem 1030 may also include other components (not shown) such asmemory, storage devices, network adapters and the like. Digitalprocessing system 1030 may be configured to generate digital diagnosticimages in a standard format, such as the DICOM (Digital Imaging andCommunications in Medicine) format, for example. In other embodiments,digital processing system 1030 may generate other standard ornon-standard digital image formats. Digital processing system 1030 maytransmit diagnostic image files (e.g., the aforementioned DICOMformatted files) to treatment planning system 2000 over a data link1500, which may be, for example, a direct link, a local area network(LAN) link or a wide area network (WAN) link such as the Internet. Inaddition, the information transferred between systems may either bepulled or pushed across the communication medium connecting the systems,such as in a remote diagnosis or treatment planning configuration. Inremote diagnosis or treatment planning, a user may utilize embodimentsof the present invention to diagnose or treatment plan despite theexistence of a physical separation between the system user and thepatient.

Treatment planning system 2000 includes a processing device 2010 toreceive and process image data. Processing device 2010 may represent oneor more general-purpose processors (e.g., a microprocessor), specialpurpose processor such as a digital signal processor (DSP) or other typeof device such as a controller or field programmable gate array (FPGA).Processing device 2010 may be configured to execute instructions forperforming treatment planning operations discussed herein.

Treatment planning system 2000 may also include system memory 2020 thatmay include a random access memory (RAM), or other dynamic storagedevices, coupled to processing device 2010 by bus 2055, for storinginformation and instructions to be executed by processing device 2010.System memory 2020 also may be used for storing temporary variables orother intermediate information during execution of instructions byprocessing device 2010. System memory 2020 may also include a read onlymemory (ROM) and/or other static storage device coupled to bus 2055 forstoring static information and instructions for processing device 2010.

Treatment planning system 2000 may also include storage device 2030,representing one or more storage devices (e.g., a magnetic disk drive oroptical disk drive) coupled to bus 2055 for storing information andinstructions. Storage device 2030 may be used for storing instructionsfor performing the treatment planning steps discussed herein.

Processing device 2010 may also be coupled to a display device 2040,such as a cathode ray tube (CRT) or liquid crystal display (LCD), fordisplaying information (e.g., a 2D or 3D representation of the VOI) tothe user. An input device 2050, such as a keyboard, may be coupled toprocessing device 2010 for communicating information and/or commandselections to processing device 2010. One or more other user inputdevices (e.g., a mouse, a trackball or cursor direction keys) may alsobe used to communicate directional information, to select commands forprocessing device 2010 and to control cursor movements on display 2040.

It will be appreciated that treatment planning system 2000 representsonly one example of a treatment planning system, which may have manydifferent configurations and architectures, which may include morecomponents or fewer components than treatment planning system 2000 andwhich may be employed with the present invention. For example, somesystems often have multiple buses, such as a peripheral bus, a dedicatedcache bus, etc. The treatment planning system 2000 may also includeMIRIT (Medical Image Review and Import Tool) to support DICOM import (soimages can be fused and targets delineated on different systems and thenimported into the treatment planning system for planning and dosecalculations), expanded image fusion capabilities that allow the user totreatment plan and view dose distributions on any one of various imagingmodalities (e.g., MRI, CT, PET, etc.). Treatment planning systems areknown in the art; accordingly, a more detailed discussion is notprovided.

Treatment planning system 2000 may share its database (e.g., data storedin storage device 2030) with a treatment delivery system, such astreatment delivery system 3000, so that it may not be necessary toexport from the treatment planning system prior to treatment delivery.Treatment planning system 2000 may be linked to treatment deliverysystem 3000 via a data link 2500, which may be a direct link, a LAN linkor a WAN link as discussed above with respect to data link 1500. Itshould be noted that when data links 1500 and 2500 are implemented asLAN or WAN connections, any of diagnostic imaging system 1000, treatmentplanning system 2000 and/or treatment delivery system 3000 may be indecentralized locations such that the systems may be physically remotefrom each other. Alternatively, any of diagnostic imaging system 1000,treatment planning system 2000 and/or treatment delivery system 3000 maybe integrated with each other in one or more systems.

Treatment delivery system 3000 includes a therapeutic and/or surgicalradiation source 3010 (e.g., LINAC 311) to administer a prescribedradiation dose to a target volume in conformance with a treatment plan.Treatment delivery system 3000 may also include an imaging system 3020to capture intra-treatment images of a patient volume (including thetarget volume) for registration or correlation with the diagnosticimages described above in order to position the patient with respect tothe radiation source. Imaging system 3020 may include any of the imagingsystems and imaging geometries described above (e.g., systems 300, 400,500, 600, 700, 800 and 900). Treatment delivery system 3000 may alsoinclude a digital processing system 3030 to control radiation source3010, imaging system 3020 and a patient support device such as atreatment couch 3040. Digital processing system 3030 may include one ormore general-purpose processors (e.g., a microprocessor), specialpurpose processor such as a digital signal processor (DSP) or other typeof device such as a controller or field programmable gate array (FPGA).Digital processing system 3030 may also include other components (notshown) such as memory, storage devices, network adapters and the like.Digital processing system 3030 may be coupled to radiation source 3010,imaging system 3020 and treatment couch 3040 by a bus 3045 or other typeof control and communication interface.

Digital processing system 3030 may implement algorithms to registerimages obtained from imaging system 3020 with pre-operative treatmentplanning images in order to align the patient on the treatment couch3040 within the treatment delivery system 3000, and to preciselyposition the radiation source with respect to the target volume.

The treatment couch 3040 may be coupled to a robotic arm (not shown)having multiple (e.g., 5 or more) degrees of freedom. The couch arm mayhave five rotational degrees of freedom and one substantially vertical,linear degree of freedom. Alternatively, the couch arm may have sixrotational degrees of freedom and one substantially vertical, lineardegree of freedom or at least four rotational degrees of freedom. Thecouch arm may be vertically mounted to a column or wall, or horizontallymounted to pedestal, floor, or ceiling. Alternatively, the treatmentcouch 3040 may be a component of another mechanical mechanism, such asthe Axum® treatment couch developed by Accuray, Inc. of California, orbe another type of conventional treatment table known to those ofordinary skill in the art.

FIG. 12 is a flowchart illustrating a method 950 in one embodiment ofimaging geometry. With reference, again, to FIGS. 3B and 3C, the methodbegins at step 951 by generating a first imaging beam 302A. At step 952,a second imaging beam 302B is generated to intersect the first imagingbeam at a first imaging center 304. At step 953, a patient 309 ispositioned at approximately the first imaging center. At step 954, afirst image is generated with the first imaging beam and a second imageis generated with the second imaging beam. At step 955, the first imageand the second image are registered with a first set of pre-treatmentreference images. At step 956, the registration result is used toposition a radiation treatment source (e.g., the LINAC 311). At step957, radiation treatment is delivered to a target anatomy in the patient309 from a first range of angles 312. At step 958, a third imaging beam303C is generated. At step 959, a fourth imaging beam 302D is generatedto intersect the third imaging beam at a second imaging center 305. Atstep 960, the patient 309 is positioned at approximately the secondimaging center. At step 961, a third image is generated with the thirdimaging beam and a fourth image is generated with the fourth imagingbeam. At step 962, the third image and the fourth image are registeredwith a second set of pre-treatment reference images. At step 963, theregistration result is used to position the radiation treatment source(e.g., the LINAC 311). At step 964, radiation treatment is delivered tothe target anatomy in the patient 309 from a second range of angles 313.

It should be noted that the methods and apparatus described herein arenot limited to use only with medical diagnostic imaging and treatment.In alternative embodiments, the methods and apparatus herein may be usedin applications outside of the medical technology field, such asindustrial imaging and non-destructive testing of materials (e.g., motorblocks in the automotive industry, airframes in the aviation industry,and welds in the construction industry and drill cores in the petroleumindustry) and seismic surveying. In such applications, for example,“treatment” may refer generally to the application of radiation beam(s).

While some specific embodiments of the invention have been shown theinvention is not to be limited to these embodiments. The invention is tobe understood as not limited by the specific embodiments describedherein, but only by scope of the appended claims.

1. An imaging system, comprising: a first pair of x-ray sources at afirst separation to generate a first x-ray beam and a second x-ray beamin an imaging plane, the first x-ray beam and the second x-ray beamdisposed to intersect at a first angle at a first imaging center; asecond pair of x-ray sources at a second separation to generate a thirdx-ray beam and a fourth x-ray beam in the imaging plane, the third x-raybeam and the fourth x-ray beam disposed to intersect at a second angleat a second imaging center; and a pair of x-ray detectors at a thirdseparation, comprising a first x-ray detector and a second x-raydetector, the first x-ray detector to detect the first x-ray beam andthe third x-ray beam, the second x-ray detector to detect the secondx-ray beam and the fourth x-ray beam.
 2. The imaging system of claim 1,wherein the first pair of x-ray sources and the second pair of x-raysources are located above the first imaging center and the secondimaging center, and wherein the pair of x-ray detectors is located belowthe first imaging center and the second imaging center.
 3. The imagingsystem of claim 1, wherein the first pair of x-ray sources and thesecond pair of x-ray sources are located below the first imaging centerand the second imaging center, and wherein the pair of x-ray detectorsis located above the first imaging center and the second imaging center.4. An imaging system, comprising: a pair of movable x-ray sources togenerate a first x-ray beam and a second x-ray beam at a firstseparation in an imaging plane, the first x-ray beam and the secondx-ray beam disposed to intersect at a first angle at a first imagingcenter, the pair of x-ray sources to generate a third x-ray beam and afourth x-ray beam at a second separation in the imaging plane, the thirdx-ray beam and the fourth x-ray beam disposed to intersect at a secondangle at a second imaging center; and a pair of x-ray detectors at athird separation in the imaging plane, comprising a first x-ray detectorand a second x-ray detector, the first x-ray detector to detect thefirst x-ray beam and the third x-ray beam, the second x-ray detector todetect the second x-ray beam and the fourth x-ray beam.
 5. The imagingsystem of claim 4, wherein the pair of movable x-ray sources is locatedabove the first imaging center and the second imaging center, andwherein the pair of x-ray detectors is located below the first imagingcenter and the second imaging center.
 6. The imaging system of claim 4,wherein the pair of movable x-ray sources is located below the firstimaging center and the second imaging center, and wherein the pair ofx-ray detectors is located above the first imaging center and the secondimaging center.
 7. An imaging system, comprising: a pair of movablex-ray sources, comprising a first x-ray source to generate a first x-raybeam and a second x-ray source to generate a second x-ray beam, at afirst separation in an imaging plane, the first x-ray beam and thesecond x-ray beam disposed to intersect at a first angle at an imagingcenter, the pair of movable x-ray sources to generate a third x-ray beamand a fourth x-ray beam at a second separation in the imaging plane, thethird x-ray beam and the fourth x-ray beam disposed to intersect at asecond angle at the imaging center; and a pair of movable x-raydetectors, comprising a first x-ray detector and a second x-raydetector, to detect the first x-ray beam and the second x-ray beam at afirst detector separation in the imaging plane and to detect the thirdx-ray beam and the fourth x-ray beam at a second detector separation inthe imaging plane.
 8. The imaging system of claim 7, the first x-raysource to track a position of the first x-ray detector from the firstdetector separation of the pair of x-ray detectors to the seconddetector separation of the pair of x-ray detectors, the second x-raysource to track a position of the second x-ray detector from the firstdetector separation of the pair of x-ray detectors to the seconddetector separation of the pair of x-ray detectors.
 9. An article ofmanufacture comprising: a machine readable medium including data that,when executed by a machine, cause the machine to perform operationscomprising: establishing a first imaging center at a first location toenable radiation treatment of a target anatomy from a first range ofangles in a treatment frame of reference; and establishing a secondimaging center at a second location to enable radiation treatment of thetarget anatomy from a second range of angles in the treatment frame ofreference.
 10. The article of manufacture of claim 9, whereinestablishing the first imaging center comprises generating a firstimaging beam having a first axis and a second imaging beam having asecond axis, the first axis and the second axis defining a first imagingplane, the second imaging beam disposed at a first angle with respect tothe first imaging beam to intersect the first imaging beam at the firstlocation.
 11. The article of manufacture of claim 10, whereinestablishing the second imaging center comprises generating a thirdimaging beam having a third axis in the first imaging plane, the thirdimaging beam disposed at a second angle with respect with respect to thefirst imaging beam to intersect the first imaging beam at the secondlocation.
 12. The article of manufacture of claim 11, wherein the thirdimaging beam is disposed at a third angle with respect to the secondimaging beam, further comprising establishing a third imaging center ata third location comprising an intersection of the second imaging beamand the third imaging beam in the first imaging plane.
 13. The articleof manufacture of claim 10, wherein establishing the second imagingcenter comprises generating a third imaging beam having a third axis anda fourth imaging beam having a fourth axis, the third axis and thefourth axis defining a second imaging plane, the fourth imaging beamdisposed at a second angle with respect to the third imaging beam tointersect the third imaging beam at the second location.
 14. The articleof manufacture of claim 13, wherein the first imaging plane and thesecond imaging plane are coplanar planes.
 15. The article of manufactureof claim 13, wherein the first imaging plane and the second imagingplane are non-coplanar planes.
 16. The article of manufacture of claim11, the method further comprising: positioning the target anatomy atapproximately the first imaging center; generating a first image withthe first imaging beam and a second image with the second imaging beam;registering the first image and the second image with a first pluralityof reference images to obtain a first registration result; positioning aradiation treatment source with the first registration result; anddelivering radiation treatment to the target anatomy from the firstrange of angles.
 17. The article of manufacture of claim 16, wherein themachine readable medium further includes data that cause the machine toperform operations comprising: positioning the target anatomy atapproximately the second imaging center; generating a third image withthe third imaging beam and a fourth image with the first imaging beam;registering the third image and the fourth image with a second pluralityof reference images to obtain a second registration result; positioningthe radiation treatment source with the second registration result; anddelivering radiation treatment to the target anatomy from the secondrange of angles.
 18. The article of manufacture of claim 12, wherein themachine readable medium further includes data that cause the machine toperform operations comprising: positioning the target anatomy atapproximately the third imaging center; generating a first image withthe second imaging beam and a second image with the third imaging beam;registering the first image and the second image with a plurality ofreference images to obtain a registration result; positioning aradiation treatment source with the registration result; and deliveringradiation treatment to the target anatomy from the third range ofangles.
 19. The article of manufacture of claim 13, wherein the machinereadable medium further includes data that cause the machine to performoperations comprising: positioning the target anatomy at approximatelythe first imaging center; generating a first image with the firstimaging beam and a second image with the second imaging beam;registering the first image and the second image with a first pluralityof reference images to obtain a first registration result; positioning aradiation treatment source with the first registration result; anddelivering radiation treatment to the target anatomy from the firstrange of angles.
 20. The article of manufacture of claim 19, wherein themachine readable medium further includes data that cause the machine toperform operations comprising: positioning the target anatomy atapproximately the second imaging center; generating a third image withthe third imaging beam and a fourth image with the fourth imaging beam;registering the third image and the fourth image with a second pluralityof reference images to obtain a second registration result; positioningthe radiation treatment source with the second registration result; anddelivering radiation treatment to the target anatomy from the secondrange of angles.